1. Field of the Invention
The invention relates to a cylindrical grooved cam made of plastic, on the inner cylindrical surface of which the grooved cams to control lens driving such as lens zooming or lens focusing of optical equipments like cameras are provided.
2. Background Art
Lenses used for optical equipments like cameras usually have a plastic made cylindrical grooved cam that has grooved cams on its inner cylindrical surface. As the said cylindrical grooved cam rotates, the lenses, which are assembled in a lens barrel and set in the cylindrical grooved cam engaging with the grooved cams through driving pin or raised portion of the lens barrel rim, are moved back and forth for focusing or moved to control the zooming according to the zooming data that are interpreted as cam data and transferred to grooved cams.
The grooved cams are formed on the inner cylindrical surface of the cylinder by plastic molding using a mold which has very complicated construction and is provided usually with a split-core slide. The mold with the split-core slide is very complicatedly designed, and the cost of the mold is extremely expensive.
After an injection of plastic material, a cylindrical grooved cam is formed having grooved cams on its inner cylindrical surface of the cylinder. Then the core-center of the slide must be pulled out of the mold so that the split-core members of the slide can be extracted out of the grooved cams formed on the inner cylindrical surface of the cylinder, and the split-core slide must be pulled out of the mold totally so that the cylindrical grooved cam can be taken out of the mold.
FIGS. 1 and 2 show a typical cylindrical grooved cam for a zoom lens, which has three grooved cams as a set to control the first group of lenses, and another set of three grooved cams to control the second group of lenses. FIG. 3 is a development of the cylindrical grooved cam to show the grooved cams provided on its inner surface.
FIG. 4 shows the first stage of molding of the cylindrical grooved cam (1) made of plastic, and the status that the plastic material has been injected into the mold (2), and the cylindrical grooved cam (1) is formed in the mold (2).
FIG. 5 shows the second stage of molding of the cylindrical grooved cam (1) and the status that core-center (3) of the split-core slide (4) has been pulled out of the mold (2).
FIG. 6 shows the third stage of molding of the cylindrical grooved cam (1), and the status that the split-core members (5) have been pulled inward coming out of the formed grooved cams (6) so that the split-core slide (4) may come out of the cylindrical grooved cam (1).
FIG. 7 shows the forth stage of molding of the cylindrical grooved cam (1), and the status that the whole split-core slide (4) has been pulled out of the mold (2) leaving the molded cylindrical grooved cam (1) inside the mold (2).
FIG. 8 shows the fifth stage (final stage) of the molding of the cylindrical grooved cam (1), and the status that the molded cylindrical grooved cam (1) with the grooved cams (6) on its inner surface has been pulled out of the mold (2).
As mentioned so far, the construction of mold is very complicated and moreover such parts like cylindrical grooved cam for camera lens driving require extreme accuracy that makes the mold making and also plastic injection very difficult and costly.
The cylindrical grooved cam that is made with the mold with split-core slide has another problem. As shown by FIGS. 9-a, 9-b, 9-c and 9-d, the grooved cams inevitably must be tapered, because the split-core members (5) (FIG. 6) of the slide of the mold must be pulled out of the grooved cams (7) smoothly. Without the taper (8), it is impossible to extract the split-core members (5) out of the grooved cams (7).
Into the grooved cams (7), the raised portions (9) of lens barrel (10), which holds a group of lenses (11) inside, are to be inserted as shown by FIGS. 9-a, 9-b, 9-c and 9-d. If a strong shock is given to the whole zoom lens, the raised portions (9) are apt to slip and come out of the grooved cams (7) due to the tapers (8) of the grooved cams (7) as shown by FIG. 10 and it jams the whole zooming control.
The extremely expensive mold with the complicated construction, the delicate and difficult plastic injection control due to the highly required accuracy, and the tapered grooved cams, which are apt to jam the zooming control by a shock, are the problems to be solved for the conventional type of cylindrical grooved cam.
Therefore it is necessary to provide an improved cylindrical grooved cam with the grooved cams provided on its inner cylindrical surface but without any tapers in the grooved cams, which can be made easily by simple molds.